The present invention relates to a laminated insulating paper composed of a cross-linked silicone grafted polyolefine film and cellulose paper or papers adhering to at least one side of the film and to an oil-filled (OF) cable insulated by the laminated insulating paper.
Recently, the development of power cables of the 500KV class has been advanced with the increased demand of electricity in cities and industrial areas.
When an electric insulating paper composed of conventional cellulose paper alone is used in such very high-voltage cables, there is such a great dielectric loss, that conventional electric insulating paper is unsuitable for use in long-distance transmission cables.
Although the use of a plastic film instead of conventional cellulose paper has been investigated, the plastic film may often craze and crack, when it is used in combination with an insulating oil for a long period of time.
In addition, the plastic film has a disadvantage that the oil flow (radial) resistance is high and thus a long period of time is required for filling the cable up with oil. Recently an electric insulating paper which is obtained by laminating polypropylene film and cellulose paper has been developed. [e.g. D. R. Edwards, D. R. G. Melville, "An Assessment of the Potential of EHV Polypropylene/Paper Laminate Insulated Self-Contained Oil-Filled Cables", IEEE 1974 Underground Transmission and Distribution Conference, Dallas, April 1974, Page 529, and K. Matsumura, H. Kubo, T. Miyazaki, "Development of Polypropylene Laminated Paper Insulated EHV Power Cables", IEEE 1976 Underground Transmission and Distribution Conference, Atlantic City, September 1976, Page 322, E. M. Allam, W. H. Cortelyou, H. C. Doepken, Jr., "Low-loss 765KV Pipe-type Power Cable" F 78 175-2. the IEEE Insulated Conductors Committee of the IEEE Power Engineering Society for presentation at the IEEE PES Winter Meeting, New York, NY, January 29 - February 3, 1978]. However, since the above-mentioned electric insulating paper is a product obtained by mere heat-adhesion of non-cross-linked propylene film and cellulose paper, the peel strength between polypropylene film and cellulose paper is decreased, when it is contacted by an insulating oil for a long period of time. Further, the polypropylene film and cellulose paper peel form each other, when the insulating paper is bent, thus resulting in wrinkles and bucklings.